Gear differentials include compound planetary gear sets carried within a differential housing interconnecting a pair of output shafts for opposite directions of rotation with respect to the housing. An input shaft is connected to the housing for rotating the housing about a common axis of the output shafts. Sun gear members of the respective planetary gear sets, also referred to as "side" gears, are coupled to inner ends of the output shafts. Planet gear members of the planetary gear sets, also referred to as "element" gears, operatively connect the two side gears for relative rotation in opposite directions.
One known arrangement of the planetary gearing positions the sun and planet gears within the housing for rotation about axes that extend parallel to each other. Differentials with this type of gearing arrangement are referred to as "parallel-axis" gear differentials. The planet gears of this type of differential are generally mounted in pairs within the differential housing. One portion of each planet gear meshes with one of the side gears, and another portion of each planet gear meshes with its paired planet gear.
The planet gears are individually supported for rotation on shafts or within pockets formed in the housings. The pockets provide bearings for slidably supporting outside cylinder surfaces of the planet gears including the top lands of the planet gear teeth. Alternatively, bores formed in the housing can be used to support opposite ends of the shafts.
Ordinarily, the planet gear pairs are evenly distributed about the central axis of the differential. The pockets supporting the element gears occupy most of the circumference of the housing, leaving little room between the pairs of pockets to form window passages through the housing to circulate lubricant or to gain access to the interior of the housing. In addition, the remaining portions of the housing between the pairs of pockets are important for preserving structural strength of the housing.
A commonly assigned copending U.S. patent application Ser. No. 735,821, filed Jul. 25, 1991, discloses an example of a parallel-axis gear differential in which the planet gears are formed as so-called "combination" gears having two gear sections separated by a stem. A first of the gear sections of each combination gear meshes with one of two side gears, and a second of the gear sections meshes with the first gear section of its paired combination gear. The two meshes between paired combination gears straddle the two meshes between the paired combination gears and the side gears.
The side gears, however, are positioned together between the straddled combination gear meshes, and this limits access to space between the side gears for fastening ends of the output shafts within the differential or for connecting a coaxial input shaft to the differential housing. In addition, relative sliding between the two side gears can produce different frictional effects between opposite directions of torque transfer through the differential housing (e.g. "drive" and "coast" directions). The opposite directions of torque transfer thrust the side gears either together or apart against opposite ends of the housing. The relative sliding velocity between the side gears is twice as great as the relative sliding velocity between either side gear and the housing.